Glycerin is obtained in large amount as a byproduct when bio-fuel is produced from bio resources that do not depend on fossil resources, and research of new uses of glycerin is under development.
We have proposed, in PCT/JP2009/057818 and PCT/JP2009/057819, an improved dehydration catalyst comprising mainly a compound in which protons in a heteropolyacid are exchanged at least partially with at least one cation selected from elements belonging to Group 1 to Group 16 of the Periodic Table of Elements.
WO2007/058221 discloses a process for producing acrolein by dehydration reaction of glycerin in gas-phase in the presence of heteropolyacid used as a solid acid catalyst. The heteropolyacid is those of Group 6 element such as tungstosilicic acid, tungstophosphoric acid and phosphomolybdic acid. These heteropolyacids are supported on bi-modal pore size distribution silica carrier and produce acrolein at a yield of 86%. This dehydration reaction of glycerin, however, is effected without oxidation gas but using nitrogen stream as carrier gas, so that deposition of carbon increase seriously and hence there is a problem of deterioration in time of stability, activity and selectivity of the catalysis.
Tsukuda et al. “Production of acrolein from glycerol over silica-supported heteropoly acid” CATALYSIS COMMUNICATIONS, vol. 8, no. 9, 21 Jul. 2007, pp 1349-1353, Chai et al., “Sustainable production of acrolein: gas phase dehydration of glycerol over 12-tungstophosphoric acid supported on ZrO2 and SiO2”, GREEN CHEMISTRY, vol. 10, 2008, pp. 1087-1093, and Chai et al., “Sustainable production of acrolein: preparation and characterization of zirconia-supported 12-tungstophosphoric acid catalyst for gas phase dehydration of glycerol”, APPLIED CATALYSIS A: GENERAL, vol. 353, 2009, pp. 213-222 disclose that silica or zirconia-supported heteropoly acid is effective as a catalyst for dehydration of glycerol.
However, there is no usable catalyst in the industrial scale at higher performance.
WO2007/058221 (Nippon Shokubai) discloses a process for dehydrating polyhydric alcohols by using a catalyst containing an element of group 6 (Cr, Mo, W), in particular, comprising a heteropolyacid which can be supported on a carrier containing Al, Si, Ti or Zr. Examples show the acrolein yield of 70% for PW/Al2O3 70% for PW/ZrO2, 87% for SiW/SiO2 but the conversion decreases from 100% to 70% in 8 hours.
U.S. patent No. 2009054538 (BATTELLE) discloses catalyst composition comprising phosphotungstic or phosphomolybdic acid on silica support and the acrolein yields obtained are not over 71% with the catalysts.
U.S. Pat. No. 5,919,725 discloses a catalyst comprising heteropoly salts and heteropolyacid salts deposited on a porous support of silica, zirconia and titania. This catalyst is used for aromatic alkylation such as alkylation of phenol with olefins but there is no mention of glycerol dehydration.
U.S. Pat. No. 4,983,565 discloses a process for preparing a catalyst composition by impregnating titania pellets with an aqueous solution consisting of tungstosilicic acid or molybdosilicic acid or their salts followed by drying and calcination. The catalyst composition is prepared preferably by impregnating a preformed pellet by immersing titania pellets in an aqueous solution of the tungstosilicic acid or molybdosilicic acid, for example. However, this patent teaches nothing about such a feature defined in the present invention that protons in the heteropolyacid are exchanged by at least one cation selected from elements belonging to Group 1 to Group 16 of the Periodic Table of Elements. Still more, this catalyst is used to prepare linear polyethylenepolyamine but there is no mention in dehydration of glycerol.